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tell(n)                      Tcl Built-In Commands                     tell(n)



tell - Return current access position for an open channel


tell channelId ______________________________________________________________________________


Returns an integer string giving the current access position in channelId. This value returned is a byte offset that can be passed to seek in order to set the channel to a particular position. Note that this value is in terms of bytes, not characters like read. The value returned is -1 for channels that do not support seeking. ChannelId must be an identifier for an open channel such as a Tcl standard channel (stdin, stdout, or stderr), the return value from an invocation of open or socket, or the result of a channel creation command provided by a Tcl extension.


Read a line from a file channel only if it starts with foobar: # Save the offset in case we need to undo the read... set offset [tell $chan] if {[read $chan 6] eq "foobar"} { gets $chan line } else { set line {} # Undo the read... seek $chan $offset }


file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3)


access position, channel, seeking Tcl 8.1 tell(n)

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